Attack on thiophen

Several other cyclizations have been achieved by intramolecular electrophilic attack on thiophene. Thus, acid-catalyzed cyclization of suitable substrates has been used to synthesize several thi-enomorphans <91H(32)107>. Interestingly, the product of cyclization of (69) depends on the acid catalyst employed. While polyphosphoric acid gives the expected (70), refluxing TFA leads to the rearranged product (71) (Scheme 15) <82CC793>. 

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